Mr Austin-Bruce was blasted multiple times in the back and torso in front of women and children also visiting the prison. He was pronounced dead at the scene.

Ross and De St Aubin, a fireman, had previously been good friends with Mr Austin Bruce. However, the relationship disintegrated to the extent that the men went on a mission to kill each other.

A few days before his murder, Mr Austin-Bruce and another youth had shot at a car being driven by De St Aubin. It was then Ross and De St Aubin plotted to kill their rival.

A prisoner known to the pair heard of Mr Austin-Bruce's intended visit to another inmate. He used a contraband mobile phone to tip off Ross and De St Aubin, and they hatched their murderous plan.

They struck as Mr Austin-Bruce and two friends were walking through the car park to the prison. A man in a suit, Ross, appeared and fired at Mr Austin-Bruce's in the back. The victim turned to face his killer, who continued to shoot him in the chest, firing six shots from close range.

Ross ran towards a nearby moped, where a getaway driver, De St Aubin, who was also dressed in a suit and crash helmet, drove off into Trinity Road.

The weapon and moped, which was stolen, were never found but witnesses identified Ross as the shooter and De St Aubin his getaway driver.

Detectives worked through phone records and found Ross was the gun-man, whose diary stated he was 'living a gangster lifestyle, making good money and living a fast life'.

After the verdict at the Old Bailey, Acting Detective Chief Inspector Brian Lucas said: "These men were living violent and criminal lives to the extent they believed they could get away with killing a man in broad daylight as revenge for a petty argument. I believe they lost sight of reality and now face the consequences of their sad and violent choices.

"I am glad today these men have been found guilty and can no longer delude themselves of their 'gangster' status, and realise a sad future is in front of them."

* The jury were unable to reach a decision on Casper Smith, 28 and Khori Hines, 34, who were also on trial for murder and will find out on Thursday if they face a re-trial.